1. Field of the Invention
The present invention relates generally to phasing and indicator arrangements for switchgear and the like in the field of electrical power distribution, and more particularly to an arrangement that facilitates phasing measurements with the use of conventional voltmeters and an indicating arrangement with desirable test features.
2. Description of the Related Art
In the field of electrical power distribution, it is a common practice to perform phasing measurements between various power cables to determine the phase difference between and the correct connection of the power cables throughout the system. Various prior art arrangements include indicator lights that respond to sensed voltage signals to indicate whether two signals are in phase or out of phase. For example, device types HOMPK and HO-PV are available from ELSIC, Trompeterallee, Germany. Further, page 14 of Merlin Gerin Publication AC0063/3E illustrates voltage indicator lamps and a phase concordance unit designated MX 403.
Additionally, various devices are known that respond to voltage sensors and that function as voltage indicators. An arrangement for testing the integrity of the voltage sensing system is shown in U.S. Pat. No. 5,521,567.
While these prior art arrangements may be useful to provide various indicator and phasing arrangements, the prior phasing arrangements are rather awkward to operate, require manipulation and interconnection of various components, require relatively expensive sensing devices, require the use of specialized meters or devices, and/or require external power supplies. Further, the prior indicator arrangements require separate power supplies for testing and do not provide simplified unambiguous self-testing functions.
Accordingly, it is a principal object of the present invention to provide an arrangement that is responsive to a voltage sensor and determines phase information that is measurable with a voltmeter.
It is another object of the present invention to provide a method to verify phasing between different electrical sources with the use of a voltmeter and such that the phasing determination is independent of the source voltage.
It is a further object of the present invention to provide a phasing arrangement that is responsive to two or more alternating current sources and that provides phasing information as the AC voltage between outputs representing each of the two of the alternating-current sources.
It is yet another object of the present invention to provide a voltage indicator arrangement for an electrical source that includes a sensorially perceptible voltage indicator and a sensorially perceptible test indicator that clearly establishes a test mode of the voltage indicator arrangement.
It is an additional object of the present invention to provide a voltage indicator arrangement that is self-powered in a test mode by a photocell.
It is a still further object of the present invention to provide a voltage indicator arrangement that includes a test mode that tests the integrity of a voltage indicator utilizing substantially the same signal that is provided during normal operation.
These and other objects of the present invention are efficiently achieved by the provision of a phasing and indicator arrangement that responds to electrical sources and provides voltage indicator functions, phasing determinations, and self-test features.
Phasing provisions are responsive to two or more voltage sensors proximate respective electrical sources to provide an output that represents the phase difference, i.e. time relationship, between the electrical sources as an alternating-current voltage measurable by a voltmeter. The output is relatively independent of the voltage of the electrical sources.
The indicator arrangement is operable in a test mode to test the integrity of one or more voltage indicators while clearly identifying that the indicator arrangement is in a test mode. In a preferred arrangement, the indicator arrangement in the self-test mode is powered by a photocell. Further, in the self-test mode, the indicator arrangement generates signals through each voltage sensor and over the complete voltage sensing path, the generated signals being substantially similar to the signals generated by each voltage sensor during normal operation in response to an alternating-current source. In the self-test mode, the phasing arrangement is also tested.